3.D.4.2.1
Cytochrome ba3 oxidase, CbaABC or CcO. The 3-d structure is known (PDB# 1EHK) (Lee et al., 2012). Proton transfer has been reviewed (von Ballmoos et al., 2012). A mutation in subunit A, D372I, a probable pump H⁺ binding site, uncouples H⁺ transport from electron flow (von Ballmoos et al. 2015). In this cytochrome ba3, O₂ molecules that arrive at the reduction site diffuse through the X-ray-observed tunnel, supporting its role as the main O₂ delivery pathway in this cytochrome ba3 as well as the cytokchrome aa3 of Rhodobacter spheroides (Mahinthichaichan et al. 2018). The proton loading site cluster in the ba3 cytochrome c oxidase that loads and traps protons has been identified (Cai et al. 2020).